The present invention relates in general to brake apparatus for use on rail cars. More particularly, the invention concerns an improved type of single cylinder, truck mounted brake apparatus, the cylinder comprising a slack adjuster.
Such single cylinder truck mounted brake apparatus have been in use for some time. For example, U.S. Pat. Nos. 3,780,837, to Haydu, and 4,060,152, to Bogenschutz et al, disclose rail car brake apparatus of this general type.
While such prior art brake apparatus have achieved a measure of success, various problems and drawbacks have been noted. In most cases, the prior art brake apparatus have been designed for use on either single axle or dual axle or triple axle trucks; so that, a given prior art brake apparatus typically cannot be readily removed from a rail car with one type of truck and installed on another with a different type of truck, without rather extensive modification.
Prior art apparatus of the type disclosed in the Haydu patent have also been criticized because of the rather large amount of pressurized fluid required to stroke their long-stroke actuators, especially those actuators having no provision for slack adjustment. Provision of long stroke capability is desirable to permit the use of thicker, longer lasting brake shoes. Where slack adjustment is provided, the prior art actuators frequently adjust only for increases in brake shoe clearance due to wear, but not for decreases in brake shoe clearance due to shoe or wheel replacement. Also, prior art slack adjusters do not begin to operate until the brake shoe engages the wheel. This delays the adjustment and possible uneveness in the brake application. Some adjusters require a number of brake application cycles before they are properly adjusted.
Another drawback of many prior art apparatus of this type has concerned the manual parking brake mechanism. Frequently, as in the older parallel beam systems, the parking brakes are applied by means of a linkage mounted on one side of the truck, to provide clearance with the central portions of the truck and bolster. Due to the off-center mounting of the parking brake linkage, the brakes tend to be applied first on the side nearer the linkage mount and then, if at all, on the side further from the linkage mount. Due to the point of force application, high stresses are induced in the beams, which must be of heavy construction. The off-center mounting also may result in application of insufficient braking force in cases where contact is made only on one side. Furthermore, crewmen checking a car to ensure parking brake application may mistakenly conclude that the brake has not been applied after looking at the shoes and wheels on the side opposite the linkage mount. In addition to the off-center mounting to clear the truck and bolster, large openings had to be cut in the bolster to allow assembly of the brake system and clearance for the cylinder and connecting rods. One prior art solution to these type of problems is disclosed by Bogenschutz et al.
Still another difficulty with such prior art apparatus has concerned the amount of disassembly required to remove and repair various elements of the apparatus. For example, it is sometimes not possible or is quite difficult to remove the actuator without disassembling a good portion of the rest of the brake apparatus.
A primary object of the present invention is to provide an improved brake apparatus or rigging for rail vehicles, the rigging being readily adaptable for use on vehicles having single, dual or triple axle trucks.
Another object of the invention is to provide an improved truck mounted brake apparatus having a fluid pressure actuated brake cylinder with a double-acting mechanical slack adjuster which automatically adjusts the clearance between the brake shoe and wheel to provide a constant clearance prior to each brake application, irrespective of brake shoe or wheel wear or replacement of shoes or wheels.
Still another object of the invention is to provide rapid take-up of the clearance after brake shoes have been replaced.
A further object of the invention is to provide a brake cylinder for such a brake apparatus, the cylinder being mounted to one of the brake beams and including means for manually stroking the actuator to apply parking brakes just as during normal application; whereby, uniform parking brake application is achieved at all wheels on both sides of the rail car truck.
Even another object of the invention is to provide a slack adjuster which permits "barring back" of the brake shoe manually to increase the shoe clearance.
Yet another object of the invention is to provide a parking brake operable by cables from a remote location to provide uniform parking brake application at all wheels.
Still another object of the invention is to provide a parallel beam brake apparatus having light weight channel-type brake beams and improved actuating and connecting linkages which minimize bending moments in the beams.
A still further object of the invention is to provide such a brake apparatus in which the light weight brake beams are attached to replaceable brake heads and in which improved spherical joints are used for connecting push rods to actuator bell crank levers.
An even further object of the invention is to provide a brake apparatus which optimizes the actuation angle of travel without modifying the truck bolster.
The above objects of the invention are intended to be only exemplary; so, other desirable objectives and advantages inherently achieved by the disclosed invention may occur or become apparent to those skilled in the art. Nonetheless, the scope of the invention is to be limited only by the appended claims.
The brake apparatus according to the invention is particularly adapted for use in rail vehicles having one, two or three transverse axles at each truck. At least one brake beam is mounted to each truck of the vehicle and extends in spaced, parallel relation to the axle for movement longitudinally of the vehicle. The brake beam includes at its opposite ends a pair of brake shoe carrying heads and each of the brake shoe carrying heads comprises a pivot means. A pair of bell crank levers is provided, each lever having a fulcrum and a pair of arms. One bell crank lever is mounted to each brake shoe carrying head with the fulcrum of the bell crank lever supported by the pivot means of the brake shoe carrying head. A fluid pressure operable brake cylinder is pivotably mounted at one end to one arm of one of the bell crank levers and at the other end to one arm of the other bell crank lever.
In such a brake rigging, one improvement of the invention comprises a pair of push rods each comprising at one end a clevis having a first axis of rotation, the clevis having arms with first bores spaced along this first axis. A spherical bearing member is positioned between the arms, the bearing member having a concave spherical bearing surface with a center of curvature positioned on the first axis. Means, such as a retaining pocket between the arms, are provided for holding the bearing member. The other arm of each of the bell crank levers has at its end a convex spherical bearing surface and a second bore having a second axis extending through the center of curvature of the convex spherical bearing surface. Means such as a pin or bolt extend through the first and second bores to pivotably couple the push rods to the bell crank levers with the spherical bearing surfaces in contact.
In accordance with another improvement of the invention, the pivot means formed in the brake shoe carrying heads comprises axially spaced bores having spaced, axially aligned and radially outwardly opening access slots. A transversely extending, outwardly opening space is defined between the axially spaced bores. The fulcrums formed in the bell crank levers include axially extending bosses or gudgeons sized to pass radially through the access slots so that the bell crank levers extend into the outwardly opening spaces and the bosses or gudgeons are positioned in the axially spaced bores. The bosses are provided with a common central bore. Bearing members rotatably support the bosses within the axially spaced bores and means such as a pin or bolt extend through the bearing members and the central bore to pivotably couple the bell crank levers to the brake shoe carrying heads. This allows positioning the pivot closer to the longitudinal center of the truck.
To provide additional support for the bell crank levers, the brake shoe carrying heads preferably comprise upwardly facing wear surfaces adjacent the lowermost of the axially spaced bores and the bell crank levers slide along these wear surfaces during brake applications and release. The other end of each push rod may be fixed to a parallel, secondary brake beam mounted adjacent a second axle in a dual or triple axle truck, or may be pivotably attached to a pull rod fixed to the same transverse axle.
The fluid pressure operable brake cylinder or actuator according to the invention comprises a housing having an interior bore within which a piston is mounted for reciprocating movement in response to pressurization and depressurization of a volume defined between the piston and the housing. A spring is positioned between the piston and the housing for biasing the piston toward a brakes-released position. A lead screw is rotatably and translatably supported at one end by the piston. Clutch means are operatively connected between the lead screw and the piston for selectively allowing or preventing rotation of the lead screw relative to to the piston. Means actuated by movement of the piston in the bore are provided for engaging the clutch means when the piston is in the brakes-released position and for releasing the clutch means as the piston moves between the brakes-released position and a brakes-applied position. The clutch means is also engaged in the brakes-applied position. A torsion power spring is operatively connected between the piston and the lead screw for rotating the lead screw or being wound by rotation of the lead screw when the clutch means is released; whereby, the lead screw is extended by the torsion spring means to take up slack, or retracted to wind the torsion spring means and provide slack, in an associated brake apparatus.
The clutch means preferably comprises a first pair of axially spaced clutch faces operatively connected to the piston, a clutch head mounted for rotation and axial translation within the piston, the lead screw being connected to the clutch head for rotation and translation therewith, and a second pair of axially spaced clutch faces operatively connected to the clutch head, the second pair being positioned between and juxtaposed to the first pair. The means for engaging, releasing and engaging the clutch means comprises a clutch operating lever pivoted to the piston, a clutch spring operatively associated with the clutch head, and a plunger slidably mounted in the piston in position to be pushed by the clutch operating lever when the lever contacts the housing. Movement of the plunger compresses the clutch spring and thereby releases one set of clutch faces from the brakes-applied position. Continued compression of the clutch spring subsequently engages the other set of clutch faces in the brakes-released position.
The lead screw is threaded through a nut, the nut being attached to a push rod slidably mounted in the housing for movement between the brakes-released and brakes-applied positions. As a result, force applied to the push rod in the brakes-released position causes the other set of clutch faces to disengage and thereby allows the lead screw to rotate through the nut and wind the torsion spring means.
In accordance with a further improvement of the invention, the actuator comprises a pair of telescope tubes attached to its piston and extending away from the volume defined between the piston and its housing. These tubes extend parallel to the lead screw of the actuator and a pair of hand brake actuator cables slidably extend into the housing and into respective ones of the telescope tubes. Means are operatively associated with the cables and the tubes for allowing the tubes to telescope over the cables when the piston moves in response to fluid pressure but for allowing the cables to move the piston toward the brakes-applied position in response to tension applied to the cables.
Other objects, advantages and novel features of tne present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.